Fibers, and particularly organic fibers, often require heat treatment to develop certain properties. Rayon fibers or fibers of polyaerylonitrile, for example, may be converted to a conductive (carbonaceous) form through high-temperature treatment. Heat is also employed in the drying of coatings or dyes upon a variety of synthetic or natural fibers.
Various ovens have been developed for the heat treatment of fibers. Certain of such ovens consist primarily of one or more aligned ceramic tubes within which a tow or plurality of fibers to be heated may pass. Such ovens generally have no provision for air or gas flow. Other ovens commonly used for treating fibers from which reaction products of the heating step or solvents or the like may be liberated employ quantities of hot air or other gases in a cross-flow pattern for contact with the fibers. The fibers commonly are supported on rolls or spools, and such ovens may be provided with a device at one end for unrolling and feeding a length of fibers into the oven, and a take-up roller or spool at the other end of the oven for winding up the heated length of fibers. As a result, the fibers traverse a given path through the oven, care being taken to avoid breaking of the fibers through undue tension as the fibers are unwound at one end and wound up at the other end. Commonly, fibers traverse horizontal paths through such ovens and the fibers may be trained around pulleys or rollers at the oven ends so as to make several traverses of the oven interior. Air or other hot gases commonly are directed generally downwardly or at an angle to the fibers in the same manner in which hot gases are flowed or jetted onto webs of material such as adhesive tape when the latter are to be heat-dried or cured. Such drafts or jets of hot gas often cause the fibers themselves to deflect and often break within the oven housing. Further, because of the positioning of hot air input and exhaust vents, the temperature within such ovens often varies considerably, the temperature being generally lower near the fiber entrance and exit ports and also near the walls of the oven.